1. Field of the Invention
This invention relates to a thermal protector mounted in a hermetic housing of a hermetic electrically-driven compressor for cutting off an electric path in response to a temperature of a refrigerant in the housing upon occurrence of an overcurrent and/or an overheat, thereby protecting an electric motor of the compressor, and more particularly to such a thermal protector which is directly mounted to a terminal assembly air-tightly mounted in a wall of the compressor housing so that the protector serves as a connector connecting between the terminal assembly and an electric motor of the compressor.
2. Description of the Prior Art
The prior art has provided various types of thermal protectors for hermetic electrically-driven compressors. These types are classified mainly depending upon manners of mounting a thermal switch with an airtight structure in a compressor housing. In one type, a terminal assembly is airtightly mounted in a wall of the compressor housing, and the thermal switch is mounted to the terminal assembly inside the compressor housing. Since the thermal switch can be easily mounted, this type has been recommended. Publication No. 5-27291 of a Japanese unexamined utility model registration application discloses this type of thermal protector. In the disclosed protector, one of terminals of the thermal switch is connected to one of lead wires of the compressor motor. A terminal strip having a receptacle at its one end is secured to the other terminal of the thermal switch. The terminal strip is inserted into a cluster socket to be fixed on an inner side wall thereof. The cluster socket and the terminal assembly are interfitted together.
The thermal switch can be easily mounted in the above-described publication. However, the thermal switch is fixed via the single terminal strip to the cluster socket. Accordingly, a force from the lead wires of the motor acts on the thermally responsive switch so as to depart the same from the cluster socket when the socket is mounted to the terminal assembly. Consequently, both terminals of the thermal switch and the terminal strip may be deformed and damaged. Furthermore, when a large thermal switch is used for a large scale compressor, mechanical vibration caused by the compressor in operation is transmitted to the thermal switch, resulting in damage of the terminals of the switch.
Publication No. 3-156183 of a Japanese unexamined patent application discloses a thermal protector in which the thermal switch is mounted to the cluster socket and thereafter, the assembly of the thermal switch and the socket is covered up by a heat-shrinkable insulating tube. In this protector, a compulsive force is not applied to the terminals of the thermal switch even when the terminals are drawn toward the lead wires of the motor. However, the insulating tube needs to be heat-shrunken in the condition that the motor is connected to the thermal switch. In this condition, heating the tube has difficulty. Furthermore, the insulating tube has apertures through which the terminals of the terminal assembly are fitted in apertures of the cluster socket. The positioning of these apertures is required when the assembly of the thermal switch and the cluster socket is covered by the insulating tube. Additionally, since the thermal switch is covered by the insulating tube, the surface of the thermal switch is not brought into direct contact with the refrigerant, which reduces the thermal responsiveness of the thermal switch.